Wavelength conversion is used for wavelength routing in photonic network systems such as Wavelength Division Multiplexing (WDM) and Optical Time Division Multiplexing (OTDM). Some of the functions it can perform include reconfigurable routing, contention resolution, wavelength reuse, multicasting, and traffic balancing. Compared with conventional optical-electrical-optical (O/E/O) wavelength conversion schemes, all-optical wavelength conversion (AOWC) is especially attractive because of the potential advantages of high speed, compactness, lower-power consumption, and high integration. Increasing demands on global delivery of high-performance network-based applications, such as cloud computing and (ultra) high definition video-on-demand streaming, requires optical networks with higher capacity and more powerful signal processing capability. This, in turn, requires wavelength conversion techniques with a broad conversion wavelength tuning range that can be used with a wide range of modulation formats.
Existing AOWC techniques can be mainly classified into two categories: optical gating and coherent mixing. Optical gating wavelength conversion techniques, such as cross gain modulation (XGM) and cross phase modulation (XPM), exploit carrier depletion and/or carrier density-induced refractive index changes so that only intensity-modulated input signals can be converted. Coherent mixing wavelength conversion techniques, such as difference frequency generation (DFG) and four wave mixing (FWM) utilize the photon conversion function in second- or third-order non-linear materials, which requires phase matching for efficient conversion. FWM-based wavelength conversion has been investigated widely in recent years in different structures, such as fibres, silicon waveguides, and semiconductor optical amplifiers, and is commonly thought of as one of the most promising AOWC techniques because of its ability to support operation using any data format. However, because FWM requires phase-matching, it suffers from poor conversion wavelength tunability.
It is desirable to provide wavelength conversion with increased tunability.